You’ll find plenty of disagreement in California’s farm community on the widely held opinion that global warming is the result of human activity. Yet farmers and their friends in agricultural research are anticipating warmer temperatures just the same.

In the current issue of the University of California’s quarterly journal California Agriculture, findings in a carefully researched article projects the effects of expected temperature increases on a range of crops grown in Yolo County.

Yolo is perhaps as typical of Central California counties as any can be, plus good temperature measurements for it are readily available.

In general, researchers Hyunok Lee and Daniel Sumner predict that extension of a slight 50 year-warming trend will cause little change in the production patterns for most tree crops grown in Yolo County. Walnuts might suffer due to a reduction in the number of winter chilling hours.   

And they say it probably will create a longer season for the huge processing tomato crop resulting in increased tonnage.

Lee, research economist with UC Davis’ Department of Agricultural and Resource Economics, and Sumner, director of UC Davis’ Agricultural Issues Center, used 100 years of temperature and climate records and 60 years of acreage data to base their conclusions.

Among the weather-based conclusions was the suggestion that improved rootstocks might well be developed to allow walnut trees, for example, to withstand and even benefit from the warming.

Adjustments by farmers to tolerate climate change will not be shocking since they’ve shifted their choices since weather data was first kept in 1913, and crop data 60 years ago.

As much due to climate changes as anything else, barley production, once a dominant crop in Yolo County, has practically disappeared. The acreage of processing tomatoes now accounts for 90 percent of the county’s vegetable acreage.

Temperature changes

One chart developed by the author’s shows that average July temperatures have declined by a degree or so over 100 years. Low temperatures in January over the same period have risen even less. 

Even so, they say the trend suggests that chill hours required by fruit and nut trees could decline from 882 hours to 712 hours by the end of the century. They suggest that temperature reduction at this scale probably will not impact grapes or almonds, but will cause a reduction in walnut production.

The study includes the examination of price differentials received if temperatures decline. The authors’ projection is that rice, among a dozen crops estimated, would be the hardest hit followed by corn second and almonds third.

Other crops considered were alfalfa, wheat, safflower, pasture, tomatoes, prunes, grapes, and walnuts, and a general category labeled ‘other fruit.’

While the study was exhaustive, the authors caution that the acreage projections were based on climate change that follows simple linear trends over the past 105 years; no unusual climate variability, extreme events, or accelerated warming. Neither did it include the market impacts that might be caused by climate change in other regions.

It is good to know that the researchers did not rely on a crystal ball for any projections. But they indicate that solid statistics of past climatic behavior might not be dependable either.

At least they eliminated one element by excluding opinions from farmers with recollections of the way temperatures used to be.